04/19/23

An Introduction to Chemistry Chapter 1

An Introduction to Chemistry Chapter 1

Eugene PasserChemistry DepartmentBronx Community College

© John Wiley and Sons, Inc

Eugene PasserChemistry DepartmentBronx Community College

© John Wiley and Sons, Inc

Version 1.0

04/19/23

1.1 What is a Science?

The observation, identification, description, experimental investigation, and theoretical explanation of natural phenomena.

“the study in which humans attempt to organize and explain, in a sytematic and logical manner, knowledge about themselves and their surroundings”

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PHYSICAL SCIENCES:Astronomy, Geology, Physics, Chemistry

SCIENTIFIC DISCIPLINES

BIOLOGICAL SCIENCES:Botany, Zoology

TODAY:Biochemistry, Molecular Biology

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• Chemistry is sometimes describes as the study of the structure and behavior of matter.

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CHEMISTRY DISCIPLINES

Analytical – what and how much (analysis)

General – fundamental laws and concepts

Inorganic – substances that are not organic

Organic – carbon and hydrogen containing compounds

Physical – energy changes in chemical reactions, theoretical

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1.3 How chemists discover 1.3 How chemists discover things - The Scientic Methodthings - The Scientic Method

The observation, identification, description, experimental investigation, and theoretical explanation of natural phenomena.

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Natural Phenomena

experimentally investigate

theoreticallyexplain

observe

describeidentify

research

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SCIENTIFIC METHOD1.Observation2.Literature research3.Hypothesis 4.Experiment 5.Theory

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DefinitionsDefinitions

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Hypothesis: A tentative explanation of certain facts (observation) that can be tested through experimentation.

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Experiment: is conducting a controlled test to collect data to support or negate a hypothesis.

• Data from experiments are called FACTS• Experiments must be conducted under carefully

controlled conditions so that they can be reproduced over and over. This separates science from pseudo science.

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Law: Statement of natural phenomena to which no exceptions are known under the given conditions. A law is not an explanation.

Theory: a statement which explains what is observed that is supported with experimental evidence and is used to make predictions. (Mathematical models are frequently derived from a theory. At any time, a new experiment may be done that invalidates the theory.)

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(tentative explanation)

(explanation based on fact)

Measurements are the data obtained from an

experiment

CH. 1.4 –MEASUREMENT and UNITS

What’s wrong with this measurement?

55.5

MEASUREMENT (cont)

Always include a numerical value and a unit

55.5 km makes more sense!

Measurements used in chemistry

length, volume, mass, time,

temperature, pressure,

concentration

The Metric System of Units

Used in scientific work, even in the US

Table 1.1

SI Units (standard metric units)

Quantity Base Unit Abbrev.

Length

Mass

Time

Temp

meter

kilogram

second

kelvin

m

kg

s

K

Amount mole mol

Symbol

l

m

t

T

n

SI Unit Prefixes

mega- M 106

deci- d 10-1

centi- c 10-2

milli- m 10-3

Prefix Symbol Factor

micro- 10-6

nano- n 10-9

pico- p 10-12

kilo- k 103

BASE UNIT --- 100

giga- G 109

GR

EA

TE

R T

HA

N

ON

E

LE

SS

TH

AN

ON

E

LENGTH (m)

• Meter is both the standard and base metric unit

• Other common length measurement:

1 mm

1 cm

1 km

10-2 m

10-3 m

103 m

0.001 m (1000 mm / 1 m) 0.01 m (100 cm / 1 m)

1000 m (0.001 km / 1 m)

• Combination of base units. (e.g., length length length)

• Standard unit is m3

• Base unit is L

• Other common units: cm3, dL, mL, μL

• Other facts:

1 cm3 = 1 mL1 dm3 = 1 L

Volume

1000 L = 1 m3

Mass

• Mass is the total quantity of matter in something.

• Determined by weight

what is weight????

• Standard unit is kg

• Base unit is g

• Other common units μg, mg, kg

Temperature

• A measure of the intensity of heat.

• It does not depend on the size of the system.

Temperature Measurement

• There are three temperature scales: Kelvin, Celsius and Fahrenheit.

• The SI unit of temperature is the Kelvin.

• In the laboratory, temperature is commonly measured with a thermometer in Celsius.

Degree Symbols

degrees Celsius = oC

Kelvin (absolute) = K

degrees Fahrenheit = oF

Exact and inexact numbers

• Exact numbers are “counting” numbers 7 days per week 12 equals one dozen “there are 32 students in this room”

• Measurements are always inexact

1.5 Reporting Values from 1.5 Reporting Values from MeasurementsMeasurements

Inexact Numbers (measurements) contain ERROR

• Systematic – controllable (faulty equipment)

• Random - uncontrollable (noise)

• Accuracy - how close a measurement is to the accepted value

• Precision - how close a series of measurements are to each other

ACCURATE = CORRECT

PRECISE = CONSISTENT

Accuracy and Precision

Choose an answerChoose an answer

1. Accurate/precise

2. Accurate/imprecise

3. Inaccurate/precise

4. Inaccurate/imprecise

A) B)

C) D)

Choose an answerChoose an answer

1. Accurate/precise

2. Accurate/imprecise

3. Inaccurate/precise

4. Inaccurate/imprecise

A)55.3 kg55.4 kg55.5 kg

B)

54.9 kg54.8 kg55.0 kg

C)

54.7 kg55.6 kg55.9 kg

D)

54.2 kg54.7 kg55.5 kg

AVG = 55.4 kg

AVG = 55.4 kg AVG = 54.9 kg

AVG = 54.8 kg

Uncertainty in measurement

• Every measurement has error associated with it.

• The more precise the measurement the less error.

• Error in a measurement is indicated by the number of significant figures in the number

• Which measurement has less error?

• Which measurement is more precise?

• Which measurement has more significant figures?

29.2oC or 29.25oC

Significant Figures

• Indicate precision of a measurement.Sig. figs. do not apply to exact numbers

• Recording Sig FigsSig figs in a measurement include the known

digits plus a final estimated digit

?.?? cm

?.?? cm

Uncertainty in measurements

• Unless otherwise stated the last digit.

• Determined from the smallest division.• Stated on the device. E.g.: ± 1, ± 0.2, etc.

• The last digit in a digital display.

• Determined from the data set.

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Counting Sig Figs

• Count all numbers EXCEPT:

Leading zeros -- 0.0025

Trailing zeros without a decimal point -- 2,500

4. 0.080

3. 5,280

2. 402

1. 23.50

Counting Sig Fig Examples

4 sig figs

3 sig figs

3 sig figs

2 sig figs